Six Lebanese soldiers have been killed in firefights as troops shelled a Palestinian refugee camp in northern Lebanon, where Islamic militants have been holed up for nearly eight weeks.

The bombardment targeting Fatah al-Islam militants began early Thursday, after more of the few remaining refugees in the camp fled. Reports say it is some of the heaviest shelling of the Nahr al-Bared camp since the standoff began. The militants responded with gunfire, ambushing soldiers on the ground.

It is not clear if the shelling marks the start of a planned Lebanese army offensive against the militants. A military source told reporters the operation is meant to increase pressure on the militants to surrender.

More than 170 people, including about 90 Lebanese soldiers, have been killed since the standoff began May 20.